This application claims the benefit of U.S. Provisional Application No. 60/295675 filed in the United States Patent Office on Jun. 4, 2001.
1. Technical Field of the Invention
The present invention relates generally to condensation cure moldmaking compositions that produce useful, curable molds and/or coatings that can be sprayed, trowled or poured, and to a method of making said molds. More particularly, the present invention relates to the use of hindered amine siloxanes to create a desirable thixotropy and cure rate in said moldmaking applications as compared to current technologies.
2. Discussion of the Related Art
Curable silicone coating compositions are well known. U.S. Pat. No. 4,460,712 describes rapid cure compositions including aminofunctional silicone compositions or silicones having alkyl radicals bearing one or more amino groups that produce curable foams and coatings. The reactive silicon group is a polyorganosiloxane that is combined with an amino functional polymer to form a silicone foam, but does not disclose or teach enhancement of thixotropic character or moldmaking.
Silicone based condensation curing mechanisms are well known to those skilled in the art, and generally involve reactions between reactants such as silanol (Sixe2x80x94OH) and siliconhydride (Sixe2x80x94H) groups; between silanol and hydrolyzable or condensable silyl groups, such as Sixe2x80x94OC(O)CH3 or Sixe2x80x94NR2, etc.; between a hydrolyzable or condensable group and a polyhydric species, such as polyamines, polyalcohols, and the like. One example of this cure system is the reaction between two polymers, one may be organic and the other may be a siloxane polymer, bearing hydrolyzable or condensable groups attached directly to silicon atom(s).
Divalent tin compounds are the most preferred condensation catalysts as described in U.S. Pat. No. 4,954,565. As taught in the art, when said condensation catalysts are used, they are added in an amount preferably from 0.01 to 20 weight parts, more preferably from 0.1 to 5 weight parts, per 100 weight parts of the silicon modified organic polymer.
Typically, silicone compositions used for moldmaking are very flowable exhibiting Newtonian-like character. Block and glove molding are the two most popular types of moldmaking in the industry. A master, or an original, is placed in a container and the catalyzed silicone is then poured over the part. The silicone is then allowed to cure after which time the original part is removed. The silicone mold is then used for reproduction of the original part. For large parts, use of the above discussed condensation cure related art for this process has severe limitations. Typically an additive for the silicone is used to make the material thixotropic, or non-flowable, so that the large part can be sprayed with the silicone or to allow for the material to be trowled onto the original.
The present invention addresses deficiencies in the current art including: undesirable changes to the cure profile, residue on the surface of the reproductions and lack of thixotropic character preventing the use of very thick layers to prepare the mold.
The present invention represents several significant advances in the art. Even though the art teaches means for producing curable silicone compositions, it does not disclose compositions with high thixotropic character or an application of the same to moldmaking.
Accordingly, it is the object of the present invention to provide a means for reducing the minimum volume of material necessary to cure silicon molds, as well as, a method wherein the curing cycle is substantially reduced.
Additional objects and advantages of the present invention are apparent from the specification, which follows.
According to the present invention, the foregoing and additional objects are obtained by providing a trowlable or sprayable condensation curable silicone moldmaking composition with thixotropic character that cures to a stable silicone mold.